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A generally oval-shaped, solid, calcareous structure that is enclosed in membranaceous sacs in the inner-ear region of the brain of vertebrates. Although there are usually three ear-stones on each side of the brain, the middle one, the sagitta, is often the largest. Because the ear-stone shows growth zones, or annual rings, it is used by fish biologists to determine the age of fish.

Subjects: Zoology and Animal Sciences.

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